Method of evaluating thermal effect of torque converter clutch slip speed calibration settings on a torque converter

ABSTRACT

A method of evaluating a thermal effect of torque converter clutch slip speed calibration settings on a torque converter includes estimating values of a plurality of vehicle operating parameters with a drive simulation model on a computer. The drive simulation model uses drive cycle inputs of a test drive cycle, and a slip speed calibration table to estimate values of the plurality of vehicle operating parameters over a pre-defined period of time for the test drive cycle. The temperature of each of a plurality of discrete regions of the torque converter are estimated with a temperature model on the computer. The temperature model uses the estimated values of the vehicle operating parameters to estimate the temperature of each discrete region of the torque converter at different times during the pre-defined period of time of the test drive cycle.

TECHNICAL FIELD

The disclosure generally relates to a method of evaluating a thermaleffect of slip speed calibration settings for a torque converter clutch,on a torque converter.

BACKGROUND

A torque converter for an automatic transmission may include a torqueconverter clutch. When an engine output and a transmission input areoperating at the same rotational speed, the torque converter clutch maybe engaged to mechanically couple an impeller of the torque converter toa turbine of the torque converter to reduce energy losses associatedwith the fluid coupling provided by the torque converter. During somedriving conditions, it is advantageous to allow a certain amount ofclutch slip across the torque converter clutch, so that the impeller andthe turbine may have a pre-defined amount of relative rotationtherebetween.

The amount of torque converter clutch slip varies with different drivingconditions. A transmission control module includes a torque converterclutch slip calibration table, which defines the desired amount ofclutch slip for the current driving conditions. The transmission controlmodule measures or senses different variables related to the currentdriving conditions, and uses those measured data points as inputs toselect the desired clutch slip from the torque converter clutch slipcalibration table. The values of the clutch slip are pre-defined, andstored in the torque converter clutch slip calibration table, in thememory of the transmission control module.

The different values for the amount of clutch slip for the differentdriving conditions must be defined to maintain an interface temperatureof the friction surfaces of the torque converter clutch below athreshold temperature level. It is important to maintain the interfacetemperature of the torque converter clutch, i.e., the temperaturebetween the friction surfaces of the torque converter clutch, totemperatures below the threshold temperature value, to preventoverheating and degradation of the transmission fluid.

SUMMARY

A method of evaluating a thermal effect of torque converter clutch slipspeed calibration settings on a torque converter of a transmission isprovided. The method includes defining a test drive cycle, whichincludes a plurality of drive cycle inputs over a pre-defined period oftime. A slip speed calibration table defines a desired amount of slip inthe torque converter clutch for differing values of a plurality ofvehicle operating parameters. Values of the plurality of vehicleoperating parameters are estimated with a drive simulation model, whichis saved in a memory of a computer. The drive simulation model uses thedrive cycle inputs of the test drive cycle and the slip speedcalibration table to estimate values of the plurality of vehicleoperating parameters over the pre-defined period of time for the testdrive cycle. A plurality of discrete regions of the torque converter aredefined, with each discrete region representing a discrete thermal massof the torque converter. The temperature of each of the plurality ofdiscrete regions of the torque converter are estimated with atemperature model, which is saved in the memory of the computer. Thetemperature model uses the estimated values of the plurality of vehicleoperating parameters during the pre-defined period of time of the testdrive cycle to estimate the temperature of each discrete region of thetorque converter at different times during the pre-defined period oftime of the test drive cycle. The estimated temperatures for eachdiscrete region of the torque converter during the pre-defined period oftime during the test drive cycle are compared to a threshold temperaturevalue, to determine if the temperature of any of the discrete regions ofthe torque converter at any time during the pre-defined time period ofthe test drive cycle were greater than the threshold temperature value.

Accordingly, a designer may evaluate the effect of torque converterclutch slip speed calibration settings on a proposed torque converterdesign, without having to physically assembly a prototype of the torqueconverter and physically test the proposed design. By defining theproposed torque converter into different discrete regions to represent aspecific thermal mass of the torque converter, and calculating orsolving energy balance equations for each discrete region with thetemperature model, the designer may simulate the thermal effect ofdifferent torque converter clutch slip speed calibration settings on thetorque converter, without having a physical prototype of the proposedtorque converter. This process improves the efficiency in the design ofthe torque converter for specific applications, by allowing the designerthe ability to easily evaluate different design options, e.g., geometry,material, line pressures, etc., without having to build and test aphysical prototype for each different design option.

The above features and advantages and other features and advantages ofthe present teachings are readily apparent from the following detaileddescription of the best modes for carrying out the teachings when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method of evaluating a thermal effect ofslip speed calibration settings for a torque converter clutch, on atorque converter.

FIG. 2 is a schematic, fragmentary, cross sectional view of a torqueconverter, showing a plurality of different discrete regions.

FIG. 3 is a schematic, fragmentary, cross sectional view of the torqueconverter showing different fluid volumes.

FIG. 4 is a schematic, fragmentary, cross sectional view of the torqueconverter showing different orifices.

DETAILED DESCRIPTION

Those having ordinary skill in the art will recognize that terms such as“above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are useddescriptively for the figures, and do not represent limitations on thescope of the disclosure, as defined by the appended claims. Furthermore,the teachings may be described herein in terms of functional and/orlogical block components and/or various processing steps. It should berealized that such block components may be comprised of any number ofhardware, software, and/or firmware components configured to perform thespecified functions.

Referring to the Figures, wherein like numerals indicate like partsthroughout the several views, a method of evaluating a thermal effect oftorque converter clutch slip speed calibration settings on a torqueconverter of a transmission is generally described. The method uses aspecialized computer to model or estimate the temperature of discreteregions of a torque converter, in order to evaluate different clutchslip speed calibrations settings and/or different configurations of thetorque converter. The evaluation process described herein is executed bythe specialized computer, thereby allowing analysis of the clutch slipspeed calibration settings and/or a proposed torque converter withoutthe need to assembly and/or test a working prototype for each specifictest.

The computer includes all software, hardware, memory, algorithms,connections, etc., necessary to execute the required steps of theprocess described herein. The computer may include one or multipledigital computers or host machines each having one or more processors,read only memory (ROM), random access memory (RAM),electrically-programmable read only memory (EPROM), optical drives,magnetic drives, etc., a high-speed clock, analog-to-digital (A/D)circuitry, digital-to-analog (D/A) circuitry, and any requiredinput/output (I/O) circuitry, I/O devices, and communication interfaces,as well as signal conditioning and buffer electronics.

The computer-readable memory may include any non-transitory/tangiblemedium which participates in providing data or computer-readableinstructions. Memory may be non-volatile or volatile. Non-volatile mediamay include, for example, optical or magnetic disks and other persistentmemory. Example volatile media may include dynamic random access memory(DRAM), which may constitute a main memory. Other examples ofembodiments for memory include a floppy, flexible disk, or hard disk,magnetic tape or other magnetic medium, a CD-ROM, DVD, and/or any otheroptical medium, as well as other possible memory devices such as flashmemory.

The controller includes tangible, non-transitory memory on which arerecorded computer-executable instructions, including a drive simulationmodel and a temperature model. The drive simulation model and thetemperature model are specialized algorithms stored in the memory of thecomputer, and are used to execute some of the steps of the processdescribed herein. The processor of the computer is configured forexecuting the drive simulation model and the temperature model.

Referring to FIG. 1, the evaluation process includes defining a testdrive cycle. Defining the test drive cycle is generally indicated by box20 shown in FIG. 1. The test drive cycle includes or defines a pluralityof drive cycle inputs over a pre-defined period of time. The drive cycleinputs simulate driver inputs into a vehicle during the pre-defined timeperiod to simulate a set of different driving and/or operatingconditions. For example, the drive cycle inputs may include a throttleposition input, a vehicle speed, a mass air inflow rate, etc. The drivecycle inputs change during the course of the pre-defined period of timeto simulate changing driving conditions, i.e., changing vehicleoperating conditions. For example, the drive cycle inputs may include afirst engine torque request at a first time, maintaining that enginetorque request for a duration, increasing the torque request at a secondtime, and then decreasing the torque request at a third time. The testdrive cycle includes all drive cycle inputs necessary to simulate theoperation of a specific vehicle in specific operating conditions duringthe pre-defined period of time.

The test drive cycle is designed/selected so as to enable assessment ofcontroller performance under various operating conditions. Simulationscenarios include events that affect the torque converter clutch slipspeed calibrations in both steady as well as transient operatingconditions, and may include various gear states, engine speeds and loadsin both towing and non-towing modes. Transient operating conditionsinclude those associated with tip-ins, gear shifts, torque converterclutch apply/release, cylinder deactivation, etc. Steady operatingconditions include those when none of the above transient events takeplace and can last for varying lengths of time. The test drive cyclecould be of long duration (simulating several hours of driving) or ofshort duration simulating specific individual or stacked high energyevents representing only a few seconds or minutes of actual drivingtime. The test drive cycle may include segments simulating drivingconditions within the city and/or over the highway. The test drive cyclemay be typically specified as vehicle speed vs time but could also bespecified as a combination of pedal and brake vs time or otherparameters such as acceleration, distance, etc. Once the test drivecycle is defined, the test drive cycle is stored in the memory of thecomputer.

A slip speed calibration table is also defined, and saved in the memoryof the computer. Defining the slip speed calibration table is generallyindicated by box 22 shown in FIG. 1. The slip speed calibration tabledefines a desired amount of slip in the torque converter clutch fordiffering values of a plurality of vehicle operating parameters.Accordingly, for any given combination of vehicle operating parameters,the slip speed calibration table defines and/or calculates the desiredamount of torque slip in the torque converter clutch. The torqueconverter slip speed values provided in the calibration tables performan important Noise Vibration Harshness (NVH) function. The torqueconverter slip speed values represent the necessary minimum slip speedsthat guarantee a level of isolation of the driveline from the enginetorque harmonics. The torsional vibrations transmitted downstreamthrough the torque converter are thereby reduced improving the NVHcharacteristics of the driveline. The torque converter slip speed valuesare defined for both steady as well as transient operating conditions.In steady conditions the torque converter slip speed values can be afunction of the load on the engine, the turbine speed, gear state,cylinder deactivation state, etc. In transient operating conditions thetorque converter slip speed values can additionally be a function ofrate of variation of the engine load. Full lockup of the Torqueconverter clutch occurs only above a calibrated vehicle speed.

Once the test drive cycle and the slip speed calibration table have beendefined and are saved in the memory of the computer, the computer thenestimates values of the plurality of vehicle operating parameters withthe drive simulation model. Estimating the values of the operatingparameters with the drive simulation model is generally indicated by box24 shown in FIG. 1. The drive simulation model is a computer model thatsimulates the operation of the vehicle at different operatingconditions. The vehicle operating parameters may include, but are notlimited to, a torque converter clutch slip speed, a torque converterclutch applied torque, a line pressure to the torque converter clutch,etc. The drive simulation model uses the drive cycle inputs of the testdrive cycle, and the slip speed calibration table to estimate values ofthe plurality of vehicle operating parameters over the pre-definedperiod of time for the test drive cycle. Accordingly, at any time duringthe pre-defined time period of the test drive cycle, the drivesimulation model estimates the values for all of the different vehicleoperating parameters. It should be appreciated that changing the drivecycle inputs will change the values of the vehicle operating parameters.Similarly, changing the slip speed calibration table will also changethe values of the vehicle operating parameters output from the drivesimulation model. Accordingly, it should be appreciated that the valuesof the vehicle operating parameters change over time during thepre-defined test period, because the drive cycle inputs change over timeduring the pre-defined test period of the test drive cycle. Theestimated values of the plurality of vehicle operating parametersoutputted by the drive simulation model are saved in the memory of thecomputer.

The values of all of the different vehicle operating parameters duringthe test drive cycle, that are outputted from the drive simulationmodel, are input into the temperature model, and used by the temperaturemodel to estimate the temperature of the torque converter for thespecific drive cycle inputs and slip speed calibration table settingsinput into the drive simulation model. Estimating the temperature of thetorque converter is generally indicated by box 26 shown in FIG. 1.However, the temperature model does not estimate the temperature of thetorque converter as a single unit. Rather, the temperature modelestimates the temperature for different, discrete regions of the torqueconverter. In order to do so, the different discrete regions of thetorque converter must be defined and saved in the memory of thecomputer. Defining the discrete regions of the torque converter isgenerally indicated by box 28 shown in FIG. 1.

Each discrete region of the torque converter represents a discretethermal mass of the torque converter. The thermal mass of each discreteregion is comprised of a thermal mass from the fluid in and circulatingthrough that specific discrete region, as well as the thermal masscontributed by the solid mass of that specific discrete region.Accordingly, a solid mass for each respective discrete region must bedefined and saved in the memory of the computer.

For example, referring to FIG. 2, a plurality of discrete regions for anexemplary embodiment of a torque converter 48 are generally shown. As isshown, the exemplary embodiment of the torque converter 48 has beenbroken into five discrete regions, i.e., a first region 50, a secondregion 52, a third region 54, a fourth region 56, and a fifth region 58.

It should be appreciated that different embodiments of the torqueconverter 48 may be discretized in a different manner, to include moreor less numbers of discrete regions. The exemplary manner in which thediscrete regions of the exemplary torque converter 48 shown in FIG. 2 isdescribed below. The details of the geometry, such as but not limited tothe length, area, volume of various parts of the torque converter 48,may be obtained from a 3D CAD model of the torque converter 48. Measuredvalues of the material properties for the solids as well as thetransmission fluid such as density, specific heat, thermal conductivity,viscosity, etc, were used.

Discretization of the torque converter 48 geometry is driven by multipleconsiderations. The finer the discretization of the geometry the higherthe accuracy of the transient simulation results. However, finerdiscretization increases the complexity of the model and also makes itcomputationally intensive to simulate over longer test drive cycles.Therefore, the intention in this effort is to achieve results ofreasonably high accuracy while keeping the model simple. Keeping in mindthese parameters, the following considerations went into thediscretization of the exemplary torque converter 48 geometry shown inFIG. 2.

The torque converter 48 geometry is treated as axisymmetric. Thestructure is sectioned along the radial direction beginning at thetorque converter 48 axis. The energy generated from friction (Hf)between the torque converter 48 clutch friction surface and the coverduring slip is added as heat to the section of the cover experiencingthe friction. This heat generation section on the torque converter 48cover is lumped as a single thermal mass, and is shown in FIG. 2 as thesecond region 52. This enables tracking of the mean temperature of thetorque converter 48 clutch. If more resolution of the temperature isdesired within the second region 52, further segmentation can be done asper desired requirements.

The energy generated from friction (H_(f)) may be calculated fromEquation 1 below.

H _(f) =T _(f)*ω_(f)   1)

Referring to Equation 1), H_(f) is the Friction Heat, T_(f) is thetorque converter 48 clutch Friction torque, and ω_(f) is the torqueconverter 48 clutch rotational slip speed.

The friction heat generation is assumed to be uniform across thefriction area. Radially varying heat distributions can be consideredalong with finer discretization of the heat generation section.

The thermal mass of each segment is assumed to be concentrated at itsmean effective radius. The mean effective radius is calculated asEquation 2 below.

$\begin{matrix}{r_{eff} = \frac{{\int{dm}} + r}{\int{dm}}} & \left. 2 \right)\end{matrix}$

Referring to Equation 2), r_(eff) is mean effective radius, m is mass,and r is radius. The length of the heat flow path between two adjoiningsegments is the sum of the segment section lengths between the masscenters of the two segments.

The first region 50 is lumped as a single thermal mass. The structure issectioned at joints in the structure and/or transition points betweendifferent materials. The third region 54 shown in FIG. 2 is a result ofa section due to a joint. A contact thermal resistance is provided atsuch interfaces.

The mass center of a segment is designed to lie at the temperaturemeasurement location. Therefore, the location of the temperaturemeasurement points also determine the sectioning of the geometry. Thefourth region 56 shown in FIG. 2 provides such a temperature measurementlocation. The fifth region 58 is lumped as a single thermal mass.

As noted above, the friction material is lumped as a single thermal mass59. The pressure plate is also sectioned in a similar way as the torqueconverter 48 cover. The section directly in contact with the frictionmaterial is lumped as one thermal mass 60. The outer section 62 and theinner section 64 are lumped as a single thermal masses.

Throughout the discretization of the torque converter 48, the BiotNumber value less than or equal to 0.1 is satisfied, which is a widelyaccepted criterion for accuracy of lumped system representation. TheBiot number value may be calculated from Equation 3 below.

Biot Number=hL/k   3)

Referring to Equation 3, h is the convective heat transfer coefficient,L is the Characteristic length of the body, and k is the thermalconductivity of material.

The temperature model uses a previous temperature value of each discreteregion of the torque converter 48 to estimate the temperature of thatdiscrete region at a subsequent time, during the test drive cycle.Accordingly, in order to enable the first temperature estimate for eachdiscrete region, an initial temperature value for each discrete regionof the torque converter 48 must be defined, and saved in the memory ofthe computer.

Once the values for all of the operating parameters have been outputfrom the drive simulation model and saved in the memory of the computer,and all necessary information defining the discrete regions of thetorque converter 48 have been input into the computer, the computer thenestimates the temperature of each of the plurality of discrete regionsof the torque converter 48 with the temperature model. As noted above,estimating the temperature of the discrete regions of the torqueconverter 48 is generally indicated by box 26 shown in FIG. 1. Thetemperature model uses the estimated values of the plurality of vehicleoperating parameters during the pre-defined period of time of the testdrive cycle to estimate the temperature of each discrete region of thetorque converter 48 at different times during the pre-defined period oftime of the test drive cycle. The estimated temperatures for eachdiscrete region of the torque converter 48 clutch, during thepre-defined period of time of the test drive cycle, that are output bythe temperature model, may be saved in the memory of the computer.

Estimating the temperature of each of the plurality of discrete regionsof the torque converter 48 with the temperature model includescalculating a volume of fluid circulating through each respectivediscrete region. The volume of fluid for each discrete region is used tocalculate the thermal mass for each discrete region that is due to thefluid in and circulating through that respective discrete region.

The temperature of each of the plurality of discrete regions of thetorque converter 48 are estimated by calculating the sum of a change intemperature over time in each respective discrete region due to thevolume of fluid circulating through each respective discrete regionduring the test drive cycle, and a change in temperature over time ofthe solid mass in each respective discrete region during the test drivecycle.

Calculating the change in temperature over time in each respectivediscrete region due to the volume of fluid circulating through eachrespective discrete region includes solving Equation 4 for each discreteregion of the torque converter 48. Equation 4 is a volumetric fluidenergy balance equation, and is provided below.

$\begin{matrix}{\frac{dT}{dt} = {\frac{\begin{matrix}{\left( {{H_{in}{\overset{.}{M}}_{in}} - {H_{out}{\overset{.}{M}}_{out}}} \right) - {H\left( {{\overset{.}{M}}_{in} - {\overset{.}{M}}_{out}} \right)} +} \\{\overset{.}{Q} + {\sum\limits_{walls}{h_{i}{A_{i}\left( {T - T_{i}} \right)}}}}\end{matrix}}{\rho \; {C_{p}\left( {V + V_{out} - V_{in}} \right)}} + {\frac{1}{\rho}\frac{dP}{dt}}}} & \left. 4 \right)\end{matrix}$

Referring to Equation 4,

$\frac{dT}{dt}$

is defined as a change in temperature over a change in time, H_(in) isdefined as the enthalpy into the discrete region, {dot over (M)}_(in) isdefined as the change in mass over time of the fluid entering thediscrete region, H_(out) is defined as the enthalpy out of the discreteregion, {dot over (M)}_(out) is defined as the change in mass over timeof the fluid leaving the discrete region, H is defined as the enthalpyof the discrete region, {dot over (Q)} is defined as the change in heatover time, h is the wall heat transfer coefficient for each discreteregion, A is the area of the wall of the discrete region, T is definedas the current temperature of the fluid, T_(i) is defined as thetemperature of the fluid at a previous time,

$\frac{dP}{dt}$

is defined as a change in pressure over a change in time, ρ is thedensity of the fluid, C_(p) is defined as the specific heat of thefluid, V is the volume of fluid in the discrete region, V_(out) isdefined as the volume of fluid leaving the discrete region, and V_(in)is defined as the volume of fluid entering the discrete region.

Calculating the change in temperature over time of the solid mass ineach respective discrete region includes solving Equation 4 for eachdiscrete region of the torque converter 48. Equation 5 is a mass energybalance equation, and is provided below.

$\begin{matrix}{{{mC}_{p}\frac{dT}{dt}} = {{\overset{.}{Q}}_{in} + {\sum{h_{i}{A_{i}\left( {T_{i} - T} \right)}}} + {\sum{\left( \frac{kA}{L} \right)_{i\_ equiv}\left( {T_{i} - T} \right)}} + {\sigma {\sum{ɛ_{i}{A_{i}\left( {T_{a}^{4} - T^{4}} \right)}}}}}} & \left. 5 \right)\end{matrix}$

Referring to Equation 5, m is defined as mass of the solid, C_(p) isdefined as the specific heat of the solid material in the discreteregion,

$\frac{dT}{dt}$

is defined as a change in temperature over a change in time, {dot over(Q)}_(in) is defined as the change in heat added over time, h is definedas the wall heat transfer coefficient for each discrete region, A isdefined as the area of the wall of the discrete region, T is defined asthe current temperature of the fluid, T_(i) is defined as thetemperature of the fluid at a previous time, k is defined as the thermalconductivity of the of the solid mass in the discrete region, L isdefined as the length of the solid mass in the discrete region, σ isdefined as Stefan-Boltman's constant (5.67*10⁻⁸ W/m²/K⁴), ε is definedas the radiation emissivity of the solid mass of the discrete region,and T_(a) is defined as the temperature of the air.

In order to determine the heat into and out of each respective discreteregion, the heat into and out of the adjoining discrete regions mustalso be known. Accordingly, estimating the temperature of a respectiveone of the plurality of discrete regions of the torque converter 48 withthe temperature model, at a respective time during the pre-defined timeperiod of the test drive cycle, includes using the temperature of atleast one other of the plurality of discrete regions of the torqueconverter 48 to estimate the temperature of the respective discreteregion of the torque converter 48 at that respective time during thepre-defined time period of the test drive cycle. For example, thetemperature of the second region 52 at a specific time is effected byand dependent upon the temperatures of the first region 50 and the thirdregion 54 at that specific time.

The process of estimating the temperature of each discrete region is anongoing, continuous process that is performed at several distinct timesduring the test drive cycle. Accordingly, the computer continuouslyredefines the temperature for each discrete region of the torqueconverter 48 during the pre-defined time period of the drive test cycleat each time increment, and then uses that redefined temperature valueto estimate the temperature value at the next time increment. Thisprocess continues for the duration of the drive test cycle. The timeincrements may be as small as possible in order to properly evaluate thethermal effect on the torque converter 48.

Once the temperature values for the different discrete regions have beenoutput from the temperature model, the estimated temperatures for eachdiscrete region of the torque converter 48 during the pre-defined periodof time during the test drive cycle may then be compared to a thresholdtemperature value. Comparing the estimated temperatures of each discreteregion of the torque converter 48 to the threshold temperature value isgenerally indicated by box 30 shown in FIG. 1. The threshold temperaturevalue is the critical temperature that the transmission fluid should notexceed in order to assure continued, proper operation of thetransmission fluid without degradation. As such, if the temperature ofone or more of the discrete regions rises above the thresholdtemperature value, then the transmission fluid may be degraded from thehigh heat, and the useful life of the transmission fluid may be reduced.The temperatures of each discrete region at all times during the testdrive cycle may be compared to the threshold temperature value todetermine if the temperature of any of the discrete regions of thetorque converter 48 at any time during the pre-defined time period ofthe test drive cycle were greater than the threshold temperature value.

The output temperature estimates from the temperature model may becompared to the temperature threshold value in any suitable manner, suchas through visual inspection, or automatically by the computer. If thecomputer compares the temperature estimates to the threshold temperaturevalue, then the computer may change a state of an indicator value, savedin the memory of the computer, to a first state. The first state is usedto indicate a positive evaluation when the temperature of all of thediscrete regions of the torque converter 48 at any time during thepre-defined time period of the test drive cycle, were not greater thanthe threshold temperature value. The computer may change the state ofthe indicator value to a second state to indicate a negative evaluation,when the temperature of any of the discrete regions of the torqueconverter 48 at any time during the pre-defined time period of the testdrive cycle were equal to or greater than the threshold temperaturevalue. The indicator value may include a value that is stored in thememory of the computer, and used to indicate the results of theevaluation process. The indicator value may be linked to and/orreferenced by an indication device, such as an alert, visual signal,screen output, etc., that is used to convey the results of theevaluation process to the technician performing the process.

The results of the evaluation process described above provides usefulfeedback to designers, allowing the designers to simulate the effect ofdesign changes, in either the torque converter 48 or the clutch slipspeed calibration settings, without having to build a physical prototypefor each design change. This evaluation process increases the efficiencyof the design process. Additionally, the evaluation process allows forthe clutch slip speed calibration settings to be easily adjusted and/ormodified until an optimum definition is decided upon. As is known, thefinal clutch slip speed calibration settings are saved in a transmissioncontrol module of a vehicle, and are used by the transmission controlmodule to control the operation of the torque converter 48 clutch duringoperation of the vehicle. Accordingly, the process described aboveprovides an improved process for providing the optimum values for theclutch slip speed calibration settings.

The heat transfer through conduction between the cover, pressure plate,turbine, impeller, etc., at the hub may be neglected. The fluid volumemay be calculated from the volume of the region enclosed naturallywithin the solid structures which contain the automatic transmissionfluid (ATF). The sectioning of the fluid domain is done to facilitatethe correct heat transfer to and from the surrounding solids. Each fluidvolume is assumed to be a homogenously mixed control volume. Referringto FIG. 3, the fluid between the friction pad and the cover is lumped asa single volume 70. While the volume of fluid lying on the release sideof the torque converter 48 is lumped as a single fluid volume 72.Similarly the volume of fluid on the apply side is lumped as a singlevolume 74. Above sectioning of the fluid domain models the heat transferwith reasonable accuracy.

Additional flow paths can be modeled using pipe elements to representthe flow through grooves when such features exist in the clutch frictionpad. The fluid flow from the release side to the apply side andvice-versa may be determined by the pressure difference across theseregions which act as boundary conditions for the flow. Flow may beassumed to be laminar. Referring to FIG. 4, the resistances encounteredby the fluid flowing through the narrow passages from the release sideto the apply side may be modeled through orifices (76, 78, 80, 84 inFIG. 4) representing the cross-section areas of passages' inlet andexit. A first orifice models the flow inlet on the release side, and isgenerally shown at 76. A second orifice represents the flow inlet, andis generally shown at 78. A third orifice represents the flow outlet tothe passage between the friction areas for the release fluid, and isgenerally shown at 80. A fourth orifice represents the flow inlet on theapply side, and is generally shown at 84.

The mass flow rate through an orifice is defined by Equation 6 below.

{dot over (m)}=c _(q) A√{square root over (2ρΔP)}  6)

Referring to Equation 6, {dot over (m)} is the mass flow rate through anorifice, c_(q) is the flow discharge coefficient, A is the cross-sectionflow area, ρ is the fluid density, and ΔP is the pressure differenceacross an orifice.

The flow resistance for flow through a passage in fluid volume Vr and Vfis modeled as an annular pipe. The centrifugal effects is added using arotating pipe element. The flow resistance for flow through Va isneglected. Flow through annular pipe may be calculated from Equation 7below.

$\begin{matrix}{Q = \frac{\pi \; {D_{o}\left( {D_{o} - D_{i}} \right)}^{3}\Delta \; P}{12 \star 8 \star {{lv}\; \rho}}} & \left. 7 \right)\end{matrix}$

Referring to Equation 7, Q is the volumetric flow rate through a pipe,D_(o) is the outer diameter of an annulus, D_(i) is the inner diameterof the annulus, l is the length of the pipe section, v is the fluidkinematic viscosity, ρ is the fluid density, and ΔP is the pressuredifference across the pipe section.

The mean fluid velocity accounting for centrifugal effects may becalculated from Equation 8 below.

$\begin{matrix}{v = \frac{\left( {{\Delta \; P} + {\rho \; {{\omega^{2}\left( {r_{2}^{2} - r_{1}^{2}} \right)}/2}}} \right)D^{2}}{32l\; \rho \; v}} & \left. 8 \right)\end{matrix}$

Referring to Equation 8, ω is the rotational speed, ρ is the fluiddensity, r₁ is the inner radius of the rotating section, r₂ is the outerradius of the rotating section, D is the hydraulic diameter of the pipecross-section, l is the length of the pipe section, ρ is the density offluid, and v is the kinematic viscosity of fluid.

The volume of fluid Vf changes during torque converter 48 clutchapply/release. This is implemented as a linear change between maximumand minimum volumes as the torque converter 48 clutch is applied orreleased. At full application of the torque converter 48 clutch, theminimum volume is specified to represent the porosity of the frictionmaterial and orifice sizes are reduced to replicate the flow through theporous material, the actual values for which is obtained from test data.

All the cover segments have conductive, convective and radiation formsof heat transfer. The friction material has convective heat transferwith the fluid, conductive heat transfer with the pressure plate andconductive heat transfer with the cover when the torque converter 48clutch is applied. The pressure plate, in addition, has convective heattransfer to the fluid. Conduction between two materials with contactthermal resistance is modeled using Equation 9) below.

$\begin{matrix}{\overset{.}{H} = {\frac{1}{\left( {\frac{l_{1}}{k_{1}A} + \frac{l_{2}}{k_{2}A} + r} \right)}\left( {T_{2} - T_{1}} \right)}} & \left. 9 \right)\end{matrix}$

Referring to Equation 9, {dot over (H)} is the heat transferred throughconduction, l₁ is the distance from geometric center of segment 1 to theinterface with segment 2, l₂ is the distance from geometric center ofsegment 2 to the interface with segment 1, A is the cross-section areathrough which conduction takes place, r is the contact thermalresistance, T₁ is the temperature of segment 1, and T₂ is thetemperature of segment 2.

Convection heat exchange may be modeled from Equation 10) below.

{dot over (H)}=hA(T _(f) −T _(s))   10)

Referring to Equation 10), {dot over (H)} is the heat transferredthrough convection, A is the surface area through which convection takesplace, T_(f) is the temperature of fluid, and T_(s) is the temperatureof segment.

Radiation heat exchange may be modeled from Equation 11) below.

{dot over (H)}=σεA(T _(a) ⁴ −T _(s) ⁴)   11)

Referring to Equation 11), {dot over (H)} is the heat transferredthrough radiation, A is the surface area through which radiation takesplace, σ is the Stefan-boltzman's constant (=5.67*10⁻⁸ W/m²/K⁴), ε isthe emission factor for the surface, T_(a) is the temperature of air,and T_(s) is the temperature of the segment.

The surface areas for convective and radiation heat transfer wereestimated from the CAD geometry. Surface of the segment wetted by thetransmission fluid is considered for convective heat transfer area,while the surface exposed to air is considered for the radiation heattransfer area. The energy lost from the hydraulic coupling of the torqueconverter 48 is added to the fluid volume Va. Power loss from torqueconverter 48 efficiency may be modeled by Equation 12 below.

{dot over (H)}=(ω₁ T ₁−ω_(t) T _(t))   12)

Referring to Equation 12), {dot over (H)} is the heat transferredthrough radiation, ω_(t) is a rotational speed, and T_(t) is thehydrodynamic torque on the impeller of the torque converter 48.

The detailed description and the drawings or figures are supportive anddescriptive of the disclosure, but the scope of the disclosure isdefined solely by the claims. While some of the best modes and otherembodiments for carrying out the claimed teachings have been describedin detail, various alternative designs and embodiments exist forpracticing the disclosure defined in the appended claims.

1. A method of evaluating a thermal effect of torque converter clutchslip speed calibration settings on a torque converter of a transmission,the method comprising: defining a test drive cycle to include aplurality of drive cycle inputs over a pre-defined period of time;defining a slip speed calibration table that defines a desired amount ofslip in the torque converter clutch for differing values of a pluralityof vehicle operating parameters; estimating values of the plurality ofvehicle operating parameters with a drive simulation model saved in amemory of a computer, wherein the drive simulation model uses the drivecycle inputs of the test drive cycle and the slip speed calibrationtable to estimate values of the plurality of vehicle operatingparameters over the pre-defined period of time for the test drive cycle;defining a plurality of discrete regions of the torque converter, witheach discrete region representing a discrete thermal mass of the torqueconverter; estimating the temperature of each of the plurality ofdiscrete regions of the torque converter with a temperature model savedin the memory of the computer, wherein the temperature model uses theestimated values of the plurality of vehicle operating parameters duringthe pre-defined period of time of the test drive cycle to estimate thetemperature of each discrete region of the torque converter at differenttimes during the pre-defined period of time of the test drive cycle; andcomparing the estimated temperatures for each discrete region of thetorque converter during the pre-defined period of time during the testdrive cycle to a threshold temperature value to determine if thetemperature of any of the discrete regions of the torque converter atany time during the pre-defined time period of the test drive cycle weregreater than the threshold temperature value.
 2. The method set forth inclaim 1 further comprising changing a state of an indicator value, savedin the memory of the computer, to a first state to indicate a positiveevaluation when the temperature of all of the discrete regions of thetorque converter at all times during the pre-defined time period of thetest drive cycle, were not greater than the threshold temperature value.3. The method set forth in claim 2 further comprising changing the stateof the indicator value, saved in the memory of the computer, to a secondstate to indicate a negative evaluation when the temperature of any ofthe discrete regions of the torque converter at any time during thepre-defined time period of the test drive cycle were equal to or greaterthan the threshold temperature value.
 4. The method set forth in claim 1wherein estimating the temperature of each of the plurality of discreteregions of the torque converter includes calculating a change intemperature over time in each respective discrete region due to a volumeof fluid circulating through each respective discrete region during thetest drive cycle.
 5. The method set forth in claim 4 wherein calculatingthe change in temperature over time in each respective discrete regiondue to the volume of fluid circulating through each respective discreteregion includes solving a volumetric fluid energy balance equation:$\frac{dT}{dt} = {\frac{\left( {{H_{in}{\overset{.}{M}}_{in}} - {H_{out}{\overset{.}{M}}_{out}}} \right) - {H\left( {{\overset{.}{M}}_{in} - {\overset{.}{M}}_{out}} \right)} + \overset{.}{Q} + {\sum\limits_{walls}{h_{i}{A_{i}\left( {T - T_{i}} \right)}}}}{\rho \; {C_{p}\left( {V + V_{out} - V_{in}} \right)}} + {\frac{1}{\rho}\frac{dP}{dt}}}$wherein $\frac{dT}{dt}$ is a change in temperature over a change intime, H_(in) is the enthalpy into the discrete region, {dot over(M)}_(in) is the change in mass over time of the fluid entering thediscrete region, H_(out) is the enthalpy out of the discrete region,{dot over (M)}_(out) is the change in mass over time of the fluidleaving the discrete region, H is the enthalpy of the discrete region,{dot over (Q)} is the change in heat over time, h is the wall heattransfer coefficient for each discrete region, A is the area of the wallof the discrete region, T is the current temperature of the fluid, T_(i)is the temperature of the fluid at a previous time, $\frac{dP}{dt}$ is achange in pressure over a change in time, ρ is the density of the fluid,C_(p) is the specific heat of the fluid, V is the volume of fluid in thediscrete region, V_(out) is the volume of fluid leaving the discreteregion, and Vin is the volume of fluid entering the discrete region. 6.The method set forth in claim 4 wherein estimating the temperature ofeach of the plurality of discrete regions of the torque converterincludes calculating a change in temperature over time of a solid massin each respective discrete region during the test drive cycle.
 7. Themethod set forth in claim 6 wherein calculating the change intemperature over time of a solid mass in each respective discrete regionincludes solving a mass energy balance equation:${{{mC}_{p}\frac{dT}{dt}} = {{\overset{.}{Q}}_{in} + {\sum{h_{i}{A_{i}\left( {T_{i} - T} \right)}}} + {\sum{\left( \frac{kA}{L} \right)_{i\_ equiv}\left( {T_{i} - T} \right)}} + {\sigma {\sum{ɛ_{i}{A_{i}\left( {T_{a}^{4} - T^{4}} \right)}}}}}};$wherein m is the mass of the solid, C_(p) is the specific heat of thesolid material in the discrete region, $\frac{dT}{dt}$ is a change intemperature over a change in time, {dot over (Q)}_(in) is the change inheat added over time, h is the wall heat transfer coefficient for eachdiscrete region, A is the area of the wall of the discrete region, T isthe current temperature of the fluid, T_(i) is the temperature of thefluid at a previous time, k is the thermal conductivity of the of thesolid mass in the discrete region, L is the length of the solid mass inthe discrete region, σ is the Stefan-Boltzman's constant (5.67*10⁻⁸W/m²/K⁴), ε is the radiation emissivity of the solid mass of thediscrete region, and T_(a) is the temperature of the air.
 8. The methodset forth in claim 1 wherein defining a plurality of discrete regions ofthe torque converter includes defining a solid mass for each respectivediscrete region.
 9. The method set forth in claim 1 wherein estimatingthe temperature of each of the plurality of discrete regions of thetorque converter with the temperature model includes calculating avolume of fluid circulating through each respective discrete region. 10.The method set forth in claim 1 further comprising defining an initialtemperature for each respective discrete region of the torque converter.11. The method set forth in claim 10 further comprising continuouslyredefining the temperature for each discrete region of the torqueconverter during the pre-defined time period of the drive test cycle.12. The method set forth in claim 11 wherein estimating the temperatureof a respective one of the plurality of discrete regions of the torqueconverter with the temperature model, at a respective time during thepre-defined time period of the test drive cycle, includes using thetemperature of at least one other of the plurality of discrete regionsof the torque converter to estimate the temperature of the respectivediscrete region of the torque converter at that respective time duringthe pre-defined time period of the test drive cycle.
 13. The method setforth in claim 1 further comprising: saving the test drive cycle in thememory of the computer; saving the slip speed calibration table in thememory of the computer; saving the estimated values of the plurality ofvehicle operating parameters in the memory of the computer; and savingthe estimated temperatures for each discrete region of the torqueconverter clutch during the pre-defined period of time during the testdrive cycle in the memory of the computer.
 14. The method set forth inclaim 1 further comprising providing the computer, with the drivesimulation model and the temperature model saved in the memory of thecomputer.
 15. A method of evaluating a thermal effect of torqueconverter clutch slip speed calibration settings on a torque converterof a transmission, the method comprising: defining a test drive cycle toinclude a plurality of drive cycle inputs over a pre-defined period oftime; defining a slip speed calibration table that defines a desiredamount of slip in the torque converter clutch for any values of aplurality of vehicle operating parameters; estimating values of theplurality of vehicle operating parameters with a drive simulation modelsaved in a memory of a computer, wherein the drive simulation model usesthe drive cycle inputs of the test drive cycle and the slip speedcalibration table to estimate values of the plurality of vehicleoperating parameters over the pre-defined period of time for the testdrive cycle; defining a plurality of discrete regions of the torqueconverter, with each discrete region representing a discrete thermalmass of the torque converter; defining an initial temperature for eachrespective discrete region of the torque converter; estimating thetemperature of each of the plurality of discrete regions of the torqueconverter with a temperature model saved in the memory of the computer,wherein the temperature model uses the estimated values of the pluralityof vehicle operating parameters during the pre-defined period of time ofthe test drive cycle to estimate the temperature of each discrete regionof the torque converter at any time during the pre-defined period oftime of the test drive cycle; wherein estimating the temperature of arespective one of the plurality of discrete regions of the torqueconverter with the temperature model, at a respective time during thepre-defined time period of the test drive cycle, includes using thetemperature of at least one other of the plurality of discrete regionsof the torque converter to estimate the temperature of the respectivediscrete region of the torque converter at that respective time duringthe pre-defined time period of the test drive cycle; comparing theestimated temperatures for each discrete region of the torque converterduring the pre-defined period of time during the test drive cycle to athreshold temperature value to determine if the temperature of any ofthe discrete regions of the torque converter at any time during thepre-defined time period of the test drive cycle were greater than thethreshold temperature value; changing a state of an indicator value,saved in the memory of the computer, to a first state to indicate apositive evaluation when the temperature of all of the discrete regionsof the torque converter at all times during the pre-defined time periodof the test drive cycle, were not greater than the threshold temperaturevalue; and changing the state of the indicator value, saved in thememory of the computer, to a second state to indicate a negativeevaluation when the temperature of any of the discrete regions of thetorque converter at any time during the pre-defined time period of thetest drive cycle were equal to or greater than the threshold temperaturevalue.
 16. The method set forth in claim 15 wherein estimating thetemperature of each of the plurality of discrete regions of the torqueconverter includes calculating a change in temperature over time in eachrespective discrete region due to a volume of fluid circulating througheach respective discrete region during the test drive cycle.
 17. Themethod set forth in claim 16 wherein calculating the change intemperature over time in each respective discrete region due to thevolume of fluid circulating through each respective discrete regionincludes solving a volumetric fluid energy balance equation:$\frac{dT}{dt} = {\frac{\left( {{H_{in}{\overset{.}{M}}_{in}} - {H_{out}{\overset{.}{M}}_{out}}} \right) - {H\left( {{\overset{.}{M}}_{in} - {\overset{.}{M}}_{out}} \right)} + \overset{.}{Q} + {\sum\limits_{walls}{h_{i}{A_{i}\left( {T - T_{i}} \right)}}}}{\rho \; {C_{p}\left( {V + V_{out} - V_{in}} \right)}} + {\frac{1}{\rho}\frac{dP}{dt}}}$wherein $\frac{dT}{dt}$ is a change in temperature over a change intime, H_(in) is the enthalpy into the discrete region, {dot over(M)}_(in) is the change in mass over time of the fluid entering thediscrete region, H_(out) is the enthalpy out of the discrete region,{dot over (M)}_(out) is the change in mass over time of the fluidleaving the discrete region, H is the enthalpy of the discrete region,{dot over (Q)} is the change in heat over time, h is the wall heattransfer coefficient for each discrete region, A is the area of the wallof the discrete region, T is the current temperature of the fluid, T_(i)is the temperature of the fluid at a previous time, $\frac{dP}{dt}$ is achange in pressure over a change in time, ρ is the density of the fluid,C_(p) is the specific heat of the fluid, V is the volume of fluid in thediscrete region, V_(out) is the volume of fluid leaving the discreteregion, and Vin is the volume of fluid entering the discrete region. 18.The method set forth in claim 16 wherein estimating the temperature ofeach of the plurality of discrete regions of the torque converterincludes calculating a change in temperature over time of a solid massin each respective discrete region during the test drive cycle.
 19. Themethod set forth in claim 18 wherein calculating the change intemperature over time of a solid mass in each respective discrete regionincludes solving a mass energy balance equation:${{{mC}_{p}\frac{dT}{dt}} = {{\overset{.}{Q}}_{in} + {\sum{h_{i}{A_{i}\left( {T_{i} - T} \right)}}} + {\sum{\left( \frac{kA}{L} \right)_{i\_ equiv}\left( {T_{i} - T} \right)}} + {\sigma {\sum{ɛ_{i}{A_{i}\left( {T_{a}^{4} - T^{4}} \right)}}}}}};$wherein m is the mass of the solid, C_(p) is the specific heat of thesolid material in the discrete region, $\frac{dT}{dt}$ is a change intemperature over a change in time, {dot over (Q)}_(in) is the change inheat added over time, h is the wall heat transfer coefficient for eachdiscrete region, A is the area of the wall of the discrete region, T isthe current temperature of the fluid, T_(i) is the temperature of thefluid at a previous time, k is the thermal conductivity of the of thesolid mass in the discrete region, L is the length of the solid mass inthe discrete region, σ is the Stefan-Boltzman's constant (5.67*10⁻⁸W/m²/K⁴), ε is the radiation emissivity of the solid mass of thediscrete region, and T_(a) is the temperature of the air.
 20. The methodset forth in claim 15 wherein defining a plurality of discrete regionsof the torque converter includes defining a solid mass for eachrespective discrete region.